X-ray-diffraction measurements have been performed on ${\mathrm{Fe}}_x{\mathrm{Mn}}_{1-x}\mathrm{}\left(001\right)\mathrm{}$ thin films strained in ${\mathrm{I}\mathrm{r}/\mathrm{F}\mathrm{e}}_x{\mathrm{Mn}}_{1-x}/\mathrm{Ir}\mathrm{}\left(001\right)\mathrm{}$ sandwiches and in $[{\mathrm{Fe}}_x{\mathrm{Mn}}_{1-x}/\mathrm{Ir}{]}_{20}$ superlattices with $x=0.7\mathrm{}$ and $x=\mathrm{0.9.}\mathrm{}$ These concentrations were chosen with regard to the magnetic properties of the alloys. Superconducting quantum interference device measurements showed a ferromagnetic state above $x\approx 0.75$ and an antiferromagnetic or a nonmagnetic one below. The samples have been investigated by using the atomic contrast available through anomalous diffraction and by recording reciprocal space maps (RSM). The (111) RSM, sensitive to both in-plane and out-of-plane parameters, has been studied as a function of the grazing incidence angle. It has revealed that the $[{\mathrm{Fe}}_{0.9}{\mathrm{Mn}}_{0.1}/\mathrm{Ir}{]}_{20}$ superlattice has a complex structure with two phases stacked along the growth axis whose origin stems from the existence of the two cubic structures (bcc and fcc) of the bulk alloys. In each case, we have shown that the ${\mathrm{Fe}}_x{\mathrm{Mn}}_{1-x}$ alloys are strained in a bct structure. This tetragonalization allows us to investigate the magnetic properties throughout a continuous transformation from a bcc phase $\mathrm{}(c/a=1\mathrm{})\mathrm{}$ to a fcc one $(c/a=\sqrt{2}).\mathrm{}$ Together with x-ray resonant magnetic reflectivity measurements, our results show that the tetragonalization plays a dominant role on the magnetic state observed for the investigated samples. For $c/a$ in the range 1.2–1.3, the Fe atoms are found to be in a ferromagnetic low-spin state.

• Received 9 September 1998

DOI:https://doi.org/10.1103/PhysRevB.60.6623